...is "Clojure":http://clojure.org/, "LFE":http://github.com/rvirding/lfe/tree etc, i.e. implementations of Lisp running on top of popular virtual machines. There are two advantages to this approach:
# You get a lot of libraries for free, as long as the author spent a bit of time thinking about interop.
# (new) Lisp code can live side-by-side with (older) Java, Erlang &c code. There is no need for a radical rewrite or any interop difficulties -- you simply write parts of your system in Lisp where it makes sense, perhaps gradually replacing older non-Lisp code.
This would also mean that:
"Common Lisp":http://en.wikipedia.org/wiki/Common_Lisp is not going to get mainstream for three reasons:
# It's full of what looks like cruft to beginners.
# It's not straightforward to get started with. Advising newbies to learn Emacs & SLIME is not wise and doesn't work. Choosing an implementation to start with can be tricky too.
# The community is not making an effort to make CL seem cool.
"PLT Scheme":http://www.plt-scheme.org/ is not a contender either, because it's perceived as little more than a Lisp for teaching, which isn't true, but the community isn't doing much to shatter this perception.
*Update* discussion over at "Hacker News":http://news.ycombinator.com/item?id=443948